In an electrophotographic image forming apparatus such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine or a printer-copier-facsimile multifunction machine, an image is generally formed on a surface of a sheet such as a paper sheet or a plastic film through the following process steps.
First, a surface of a photoreceptor body having photoelectric conductivity is evenly electrically charged and, in this state, exposed to light, whereby an electrostatic latent image corresponding to an image to be formed on the sheet is formed on the surface of the photoreceptor body (charging step and exposing step).
Then, toner (minute color particles) preliminarily electrically charged at a predetermined potential is brought into contact with the surface of the photoreceptor body. Thus, the toner selectively adheres to the surface of the photoreceptor body according to the potential pattern of the electrostatic latent image, whereby the electrostatic latent image is developed into a toner image (developing step).
Subsequently, the toner image is transferred onto the surface of the sheet (transfer step), and fixed to the surface of the sheet (fixing step). Thus, the image is formed on the surface of the sheet.
Further, a part of the toner remaining on the surface of the photoreceptor body after the transfer of the toner image is removed, for example, by a cleaning blade or the like (cleaning step). Thus, the photoreceptor body is ready for the next image formation.
In the developing step out of the aforementioned process steps, a developing roller is used for developing the electrostatic latent image formed on the surface of the photoreceptor body into the toner image.
A known developing roller is produced, for example, by blending an ion conductive rubber such as an epichlorohydrin rubber with a diene rubber such as a styrene butadiene rubber (SBR) or a chloroprene rubber (CR) as a rubber component to prepare an ion conductive rubber composition, forming the rubber composition into a tubular body, crosslinking the rubber component of the tubular body, and further forming an oxide film on an outer peripheral surface of the tubular body by UV irradiation (Patent Document 1 and the like).